This invention relates to fluids used in treating a subterranean formation. In particular, the invention is oilfield treatment fluids containing a gas component and fibers, and uses thereof.
Various types of fluids are used in operations related to the development, completion, and production of natural hydrocarbon reservoirs. The operations include fracturing subterranean formations, modifying the permeability of subterranean formations, or sand control. The oilfield stimulation fluids employed in these operations are known as drilling fluids, completion fluids, work over fluids, packer fluids, fracturing fluids, drilling fluids, conformance or permeability control fluids, and the like.
Fluid technologies incorporating a gas component to form a foam or energized fluid are commonly used as oilfield treatment fluids. For example, some viscoelastic fluids used as fracturing fluids contain a gas such as air, nitrogen or carbon dioxide to provide an energized fluid or foam. Other common uses of foams or energized fluids include wellbore cleanout, gravel packing, acid diversion, fluid loss control, and the like.
Foam or energized fluids are stable mixtures of a gas phase and liquid phase. It is generally believed that a surfactant stabilizes the thin liquid films that form the surface of foam cells, thus reducing coalescence. The foam or energized fluids expand and flow back from the well and force the fluid out of the fracture, consequently ensuring an improved clean-up.
Foam and energized fracturing fluids are generally described by their foam quality, i.e. the ratio of gas volume to the foam volume. If the foam quality is between 52% and 95%, the fluid is conventionally called foam, and below 52%, an energized fluid. In the present patent application, the term “energized fluid” is used however to describe any stable mixture of gas and liquid, notwithstanding the foam quality value.
Hydraulic fracturing is a stimulation treatment routinely performed on oil, gas and other wells to increase fluid production from reservoirs. Specially engineered fluids, including energized fluids viscosified with viscoelastic surfactants or even polysaccharide derivatives (i.e. guar), are often pumped at high pressure and rate into the reservoir interval to be treated, causing a fracture to open. Proppant, such as ceramic beads or grains of sand of a particular size, is slurried with the treatment fluid (usually therefore called a carrier fluid) to keep the fracture open when the treatment is complete. Hydraulic fracturing creates high-conductivity communication with a large area of a formation and bypasses any damage that may exist in the near-wellbore area. It is therefore important for the treatment fluid to have viscosity properties sufficient to suspend and carry the proppant into the fracture zone. In some cases, however, depending upon specific subterranean formation conditions or job designs, energized fluids may not have high enough viscosity to achieve optimum proppant transportation and suspension, thereby resulting in poor proppant placement. Increased levels of viscosifying agent, or surfactants, or higher foam quality may be required to achieve adequate proppant placement, leading to increased resource and material requirements.
Foam or gas phase stability is important when using energized fluids for oilfield treatments. It is generally known that stability is improved by increasing the viscosity of the liquid phase, thus making the gas bubbles more difficult to move together and subsequently coalesce. Adding more viscosifying agent is a common method to help stabilize an energized fluid. Unfortunately, this approach also leads to the need for increased levels of viscosifying agent, and can cause increased polymer damage to the formation.
Therefore, the need exists for energized fluids for oilfield treatment with significant stability, excellent proppant transport and suspension capability, as well as providing improved cleanup properties. A fluid that can achieve the above would be highly desirable, and the need is met at least in part by the following invention.